This invention relates to the inhibition of chemical toxicity and carcinogenesis by sustained release derivatives of D-glucaro-1,4-lactone. D-glucaro-1,4-lactone is a naturally occurring compound and is known to be a potent inhibitor of .beta.-glucuronidase in vitro (Levvy, G. A. Biochem. J., 52:464-470, 1952). It is known that most chemical carcinogens and tumor promoters are trapped in the form of a glucuronide, which is then excreted from the body. This process, glucuronidation, is a principal conjugation pathway in vertebrates. The conjugates of xenobiotics, including carcinogens and promoters, are excreted via the bile and urine. The elimination of potentially damaging chemicals which undergo glucuronidation is not only limited by their rate of conjugation with glucuronic acid, but also by their rate of de-glucuronidation by the ubiquitous enzyme .beta.-glucuronidase, which hydrolyzes the carcinogen-glucuronide conjugate, and thereby frees the carcinogen to inflict damage and produce neoplastic transformations.
Glucuronyl transferase, which catalyzes glucuronidation (a major pathway of detoxification), and .beta.-glucuronidase, which catalyzes de-glucuronidation, appear to be present in all mammalian tissues. Thus, any factor which alters the ratio of these two enzymes may alter the susceptibility of the target tissue to chemical carcinogens or promoters.
Chemical carcinogenesis exhibits two main steps in the multi-step process of tumorigenesis, an irreversibly initiating phase and a subsequent reversible promotion phase. These two phenomena are discrete and temporally separable. Since the identification of experimental promoting agents such as croton oil in skin carcinogenesis, phenobarbital in hepatocarcinogenesis, and saccharin in bladder carcinogenesis, a major focus of carcinogenesis is now on the promotion phase of chemical carcinogenesis. The elimination or reduction of all environmental and endogenous carcinogens and promoters to which the human populations are at risk presents a formidable task. The identification of nontoxic inhibitors of one of the phases of the carcinogenic process, particularly those of natural origin, are most relevant to this problem.
As one example, polynuclear aromatic hydrocarbons (PAHs) are widespread environmental pollutants, which occur in the atmosphere, water and food and also in tobacco smoke. PAHs are strongly suspected of causing cancer in man. Primary metabolites of PAHs, such as epoxides, dihydrodiols and phenols as well as their secondary metabolites such as diol-epoxides are detoxified through coupling with glutathione, sulfuric acid and glucuronic acid. Also, certain toxic chemicals, such as TCCD (dioxin) are known to undergo glucuronidation in the body. It is known that conjugation with glucuronic acid, i.e. glucuronidation, is the principal conjugating pathway in vertebrate species examined over a wide range of tissues and accounts for most of the conjugated detoxified material in bile and urine. Thus, although D-glucaro-1,4-lactone appears to be present in all tissues and fluids of the body, it is thought to be of limited value in vivo since it is only present in low concentrations in subpopulations thought to be at high risk for cancer, and is cleared from the body too rapidly to be very effective.
In the past, attempts have been made to use GL to prevent the experimental induction of bladder cancer with 2-naphthylamine in dogs (Boyland et al., Invest. Urol., 2:439-445 1965), however without any success. The use of GL was based on the concept of inhibition of the enzyme .beta.-glucuronidase in mammalian urine and thus prevention of enzymic hydrolysis of glucuronides of 2-naphthylamine carcinogenic metabolites in the bladder. A similar attempt using 2-acetylaminofluorene as a carcinogenic agent with GL in rats, was also unsuccessful (Bradley, J. Urol., 88:626-628, 1962). GL was rapidly metabolized and less than 50% of the administered compound was excreted unchanged in urine and the excretion was also rapid. GL in both of the experiments cited above was given to animals at the same time as carcinogens, i.e. too late to be effective.
The European Pat. No. 1,066,885 shows the use of 2,5-di-O-acetyl-D-glucosaccharo-1,4-3,6-dilactone (DAGDL), a synthetic precursor of GL, as a therapeutic agent for the treatment of several diseases, such as diabetes, rheumatoid arthritis, toxemia in pregnancy and bladder cancer. However, a review of the medical literature shows that the attempts to use DAGDL in the treatment of such diseases were unsuccessful. For example, the effect of 2,5-di-O-acetyl-D-glucaro-1,4;6,3-dilactone (DAGDL), a potent in vivo .beta.-glucuronidase inhibitor (Iida et al., Jpn. J. Pharmacol., 15:88-90, 1965) on the induction of bladder tumor with 2-acetylaminofluorene (2-AAF) was studied in rats (Miyakawa et al., Invest. Urol., 10:256-261, 1973). Again, DAGDL was given to animals at the same time as the carcinogen 2-AAF, and statistical analysis of the tumor incidence data did not disclose any significant difference between DAGDL-treated and control rats.
An attempt to inhibit, with DAGDL, N-butyl-N-(4-butanol)nitrosaminemediated induction of bladder tumor in the rat was also unsuccessful (Uemura et al., Nishi Nippon Hinyokika 37:327-342, 1975; Chem. Abstr., 86:41460u, 1977).
In a recent study, a synthetic inhibitor of .beta.-glucuronidase failed to reduce tumor incidence in azoxymethane-induced colonic carcinogenesis in rats (Takado et al., Cancer Res., 42:331-334 1982) because it was administered at the same time as a carcinogen.
A clinical trial of GL in an attempt to prevent the development of bladder tumors in patients, who had previously had bladder cancer, failed to show any clear beneficial effects of GL (Boyland et al., Brit. J. Urol., 36:563-569, 1964). A similar trial using DAGDL instead of GL showed only a slight beneficial effect (Katayama, Jpn. J. Urol., 63:951-971, 1972). In these studies GL or DAGDL were used as chemotherapeutic agents rather than as anti-carcinogens.
Use of DAGDL to increase clearance of antibiotics which cause kidney damage (Furuno et al., U.S. Pat. No. 3,928,583, 1975) showed inconclusive results.
The above prior uses expressly illustrate that DAGDL and GL, were not effective as therapy in the treatment of various existing diseases, such as cancer, since the DAGDL or GL compounds were administered after the disease was already present in the subject.
Walaszek, et al., Carcinogenesis, 1984, 5:767-772, showed the use of DAGDL, as an inbititor of the initiation phase of carcinogenesis where the initiation of a tumor, caused by exposure to the carcinogen 7,12-dimethylbenzanthracene (DMBA), was inhibited by the administration of DAGDL. It was disclosed that the inhibition of .beta.-glucuronidase increased the proportion of the carcinogen DMBA which was sequestered and excreted as the glucuronide and decreased the proportion of the carcinogen available for activation of the proximal carcinogen; however, there was no indication that DAGDL could also act to inhibit the totally unrelated promotion phase of carcinogenesis since the promotion phase of carcinogenesis most often occurs at a later period in time, often years after the initiating event of exposure to the carcinogen. Further, since DAGDL is a synthetic compound, it would not be widely accepted by the consuming public for use in the prevention of the initiating phase of carcinogenesis.
Therefore, there is a need for anticarcinogenic agents and antipromoters which will show sustained in vivo activity.
There is a further need for inhibitors of chemical toxins and carcinogens which undergo glucuronidation in the body and are acceptable to the general population.
There is a further need for reducing cancer incidence in high risk subpopulations by administration of sustained release precursors of GL in order to raise the body levels of GL.